//起始时间
//1980年1月1日星期二
//前面有两个空位
//一年有 365天 366天
//计算今年是365天还是366天

var year = 2019;
var mounth =5;


document.querySelector("#nian").innerHTML = year;
document.querySelector("#yue").innerHTML = mounth;

//总天数
var days =0;

//判断这一年是不是闰年
function runNian (y){
    if(y % 400 === 0 || (y % 4 === 0 && y % 100 !== 0)){
        return true;
    }else{
        return false;
    }
}

//算1980年到现在的头一年有多少天
for(var i =1980; i<year; i++){
    if (runNian(i)){
        days  += 366 ;
    }else {
        days += 365 ;
    }
}

//今年的1月到这个月的上个月有多少天
for(var k = 1; k<mounth; k++){
    switch (k){
        case 1:
            days += 31;
            break;
        case 2 :
            if (runNian(year)){
                days += 29;
            } else {
                days += 28;
            }
            break;
        case 3:
            days +=31;
            break;
        case 4:
            days +=30;
            break;
        case 5:
            days +=31;
            break;
        case 6:
            days +=30;
            break;
        case 7:
            days +=31;
            break;
        case 8:
            days +=31;
            break;
        case 9:
            days +=30;
            break;
        case 10:
            days +=31;
            break;
        case 11:
            days +=30;
            break;
        case 12:
            days +=31;
            break;
    }
}

//算一下本月一共有多少天
var day = 0 ;
switch (mounth){
    case 1:
        day += 31;
        break;
    case 2 :
        if (runNian(year)){
            day += 29;
        } else {
            day += 28;
        }
        break;
    case 3:
        day +=31;
        break;
    case 4:
        day +=30;
        break;
    case 5:
        day +=31;
        break;
    case 6:
        day +=30;
        break;
    case 7:
        day +=31;
        break;
    case 8:
        day +=31;
        break;
    case 9:
        day +=30;
        break;
    case 10:
        day +=31;
        break;
    case 11:
        day +=30;
        break;
    case 12:
        day +=31;
        break;
}

console.log(day);

//算一下上个月一共有多少天
var prevDay = 0;
if (mounth == 1){
    prevDay +=31;
}else{
    switch (mounth - 1){
        case 1:
            prevDay +=31;
            break;
        case 2:
            if (runNian(year)){
                prevDay +=29;
            }else {
                prevDay +=28;
            }
            break;
        case 3:
            prevDay +=31;
            break;
        case 4:
            prevDay +=30;
            break;
        case 5:
            prevDay +=31;
            break;
        case 6:
            prevDay +=30;
            break;
        case 7:
            prevDay +=31;
            break;
        case 8:
            prevDay +=31;
            break;
        case 9:
            prevDay +=30;
            break;
        case 10:
            prevDay +=31;
            break;
        case 11:
            prevDay +=30;
            break;
        case 12:
            prevDay +=31;
            break;

    }
}



console.log(prevDay);

//因为19800101是从星期二开始的，我想让他从星期日开始算，所以
days +=2;
console.log(days);

//算出本月的1号是星期几（算出起始位置）
var start = days % 7;
console.log(start);

//算一下当前页面的日历一共可以放多少天
var num =42;

var nextDays = num -start -day;

//取到今天是几号
var thisdate = new Date().getDate();

var date1 = document.querySelector("#date1");

for(var j = prevDay -start +1;j<=prevDay; j++){
    date1.innerHTML +="<span class='h'>"+ j +"</span>";
}

for(var a = 1; a<=day; a++){
    if (a==thisdate){
        date1.innerHTML +="<span class='today'>"+a+"</span>";
    }else {
        date1.innerHTML +="<span>"+a+"</span>";
    }
}

for (var s=1; s<=nextDays; s++){
    date1.innerHTML +="<span class='h'>"+s+"</span>";
}

//先算1980-2018年一共多少天
//再算2019年1月-4月一共多少天
//再算本月一共有多少天
//根据余数算出前面有几个空位
//补充上末尾有几个空位，用for循环补充上